You say: “I’m not currently experiencing fires, but I keep reading “don’t leave it unattended, have an extinguisher, you will get a fire” etc. So I’m trying to be prepared. Unless I’m overthinking it?”
But in your original question, you said: “Small flames tend to go away when I’m cutting acrylic, . . .”
You are experiencing fires!
Like many others said, a combination of the right speeds and power settings plus air assist should inhibit fires. You don’t want to cut using max power along with very slow speed to cut thick or very thick material, instead use 2 or more passes to accomplish the cutting job.
I’ve had a flame jetting out from under some acrylic (maybe the protective film?) which disappeared within half a second, but I was more concerned with fires that need dealing with. As you say, should that occur I will know the power/speed is wrong, and I’ll make a note of that for future reference, but in that moment I’m probably going to want to put the fire out, hence the question about best practice. Once I’ve got all my material settings dialled in, I don’t expect to see flames.